Image correlator with image shift detection capability

ABSTRACT

This invention relates to an electro-optical system capable of determining the transtational shift of one image of a given scene with respect to another image obtained a short time before. This is accomplished by measurement of the amount of electrons impinging on phosphor screen 30 from a particular direction.

United States Patent Hecker 1 Mar. 27, 1973 [54] IMAGE CORRELATOR WITHIMAGE [56] References Cited SHIFT DETECTION CAPABILITY UNITED STATESPATE Ts lnventori Klaus Heck", Riverside, Calif- 2,550,316 4 1951 Wilder..313 67 2,916,661 12 1959 Davis. [73] Assgnee' r g' g fi tagg s?2,969,477 l/l96l Gfibel p y y 2,992,346 7/1961 Farnsworth ..31s 11 xNavy [22] Filed: Aug. 28, 1964 Primary ExaminerCarl D. QuarforthAssistant ExaminerP. A. Nelson [21] Appl' 394380 Attorney-Q. BaxterWarner, J. M, St. Amand and T.

M. Phillips [52] U.S.Cl.... ..3l5/ ll,3l5/l2,315 /31,

178/72, 313/68 R, 313/74, 343/77 [57] ABSTRACT [51] Int. Cl. ..H0lj31/48 58 Field of Search ..315/10, 11, 12, 14, 31; relates elect mealSystem 313/67, 68, 74;.343/7.7, 100.7 UX;178/7.2 A; 340/1463; 88/1, 14;346/110; 88/14 E; 324/77 T capable of determining the transtationalshift of one image of a given scene with respect to another imageobtained a short time before. This is accomplished by measurement of theamount of electrons impinging on phosphor screen 30 from a particulardirection.

3 Claims, 2 Drawing Figures PROGRAMMER POWER SUPPLY Patented March 27,1973 231B; (-22; IlllllllllllIIIIIIIIIIIIIIIIIMIIIllllllillllp IPROGRAMMER POWER SUPPLY SIZE OF VIRTUAL IMAGE FIG./

SIZE OF STORED IMAGE KLAUS J. HECKER INVENTOR.

IMAGE CORRELATOR WITH IMAGE SHIFT DETECTION CAPABILITY The inventionherein described may be manufactured and used by or for the Governmentof the United States of America for governmental purposes without thepayment of any royalties thereon or therefor.

The present invention relates to image correlator and the method ofcorrelating images electronically.

This invention relates to an electro-optical system capable ofdetermining the translational shift of one image of a given scene withrespect to another image obtained a short time before. The referenceimage is stored on a storage electrode in a novel vacuum tubearrangement. The image to be compared is focused onto a different planethan that of the storage electrode. Effectively, the two images aresuperimposed and electrons are allowed to pass through to the viewingscreen and excite a spot in the direction of best match" of the twoimages. The deviation of the spot is a measure of the shift of the imageover the time of a cycle of operation of the device.

Accordingly an object of the invention is to provide a means and methodof the electronic correlation of two images.

Other objects and many of the attendant advantages of this inventionwill become readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

FIG. 1 is a schematic cross-sectional view of an image correlating tubeincorporating one embodiment of the invention.

FIG. 2 is a diagram showing the focusing in a plane of an image releasedfrom the photocathode of the tube of FIG. 1.

Referring now to the drawing, the image comparing device is providedwith an evacuated envelope which contains various electrodes to bedescribed below. As shown in FIG. 1, a light image from object 12 isfocused by means of a suitable lens 14 onto a photocathode 16, which inresponse to said light image, emits a corresponding electron image. Theelectron image is directed by suitable means, such as by focusing coil18 and accelerating electrode 20 onto a storage electrode 22. Storageelectrode 22 consists of a back plate 24 and a dielectric 26 which maybe of the type used in the recording storage tubes (CK7571). A secondfocusing coil 28 and a fluorescent screen 30 are provided to focus andview the stored image. All electrodes of tube 10 are connected to aprogrammable power supply 32 which provides the necessary voltages forthe different electrodes of the tube. Power supply 32 is connected to aprogrammer 34 which determines the sequence of the different programmodes described below. Programmer 34 may be manually operated.

When tube 10 is operated in the erase mode, photocathode 16 is uniformlyilluminated by a light source 36 and all the electrode voltages andfocusing means are adjusted so as to remove all charges from storagescreen 22. In this mode, electrons are released from electrode 16 andflood storage screen 22 in such a way that either by secondary emissionfrom storage screen 22 or by electron bombardment induced conductivityof storage screen 22, all charges are removed from electrode 22.

When operated in the store mode, an image from the scene 12 is focusedby lens 14 onto electrode 16. By properly adjusting the electrodevoltages and the focusing coils, the emitter photoelectrons fromelectrode 16 are electronically focused onto storage screen 22 and willcause a change in the distribution of electrons on screen 22. Thisdistribution of electrons will remain as a stored image which may be ofeither negative or positive polarity. The size of this stored image neednot be of the same size as the image on electrode 16.

Next, tube 10 is operated in the viewing mode where again electrode 16is uniformly illuminated by light source 36. Focusing coil 18,accelerator 20 and storage screen 30 are adjusted so that no change inthe electron distribution of storage screen 22 will result. Electrode 22is now uniformly illuminated by flood electrons from photocathode 16.Storage screens should be selected of the types that have the propertyof permitting a larger or smaller flow of electrons through the screen22 depending on the charge stored thereon. As a result, the pattern ofelectrons released from electrode 22 will be similar to the pattern ofelectrons released from electrode 16 during the store mode. By theproper adjusting of focusing coil 28, this electron image is focusedonto phosphor screen 30 which is identical to the stored image and canbe viewed by an operator. The above described three functions, erasemode, store mode, and viewing mode are functions well known in the artand may be as shown and described in U.S. Pat. No. 2,992,346.

When operated in the correlation mode, electrode voltages and focusingcoils l8 and 28 are adjusted so that the electron image fromphotocathode 16 is focused into a plane which is not common with thestorage screen 22. While several different arrangements are possibledepending upon the particular spacing of the elements in the tube, twoexamples of the correlation mode are described below.

In the first example, the electron image released from electrode 16 maybe focused into a plane 38 between accelerator electrode 20 and storagescreen 22 (See FIG. 2). Focusing coil 28 and the electrode voltages inthe right half of the tube should be adjusted so that there will be nofurther acceleration of the electrons leaving the image plane betweenelectrode 20 and electrode 22. Since electrons from the different spotsof electrode 16 will be released in practically all directions (to therear of electrode 16), the same will be true for the electrons leavingthe image plane between electrodes 20 and 22. Focusing coil 18 and theelectrode voltages in the left section of the tube are adjusted so thatthe virtual image is larger than the stored image on storage screen 22.With electrons leaving in all directions from the virtual image 38,electrons will be allowed to penetrate storage screen 22 depending uponthe charge stored thereon. Depending upon whether or not the two imagesin a particular direction match, a certain amount of electrons will hitphosphor screen 30 in this particular direction. As shown in FIG. 2, thesize of virtual image 38 is larger than the size of the stored image onstorage screen 22. This geometry will cause the electron passing throughscreen 22 to converge at the spot 40 on phosphor screen 30. Analogous tothe matching of transparencies described in U. S. Pat. No. 2,787,188,the number of electrons will be largest or smallest in the direction ofbest match depending upon whether a negative or positive image wasstored on the electrode 22 during the store mode. The deviation of thecorrelation spot 40 (FIG. 2) on screen 30 is a measure of thetranslational shift of the image of scene 12 on photocathode 16 betweenthe time this image was stored in the store mode and the image iscorrelated in the correlation mode.

In the second example, focusing coil 28 is adjusted to act as anelectron lens to form a visual image between electrodes 20 and 22 whichwould be smaller than the image stored on electrode 22. The remainder ofthe operation is identical to that described in example one above.

Various modifications may be made in the practice of the invention.Light source 36 may be arranged in a ring around tube in back or infront of electrode 16. In one form the ring of light may be a band ofelectroluminescent material on envelope 10.

Light source 36 may also be replaced by an electron flood gun insideenvelope 10.

Photocathode 16 may be sensitive in the ultra-violet, in the visibleand/or in the infrared portion of the electromagnetic spectrum.

The electrode for electrostatic focusing may be formed by coating theinside of tube 10 with a conductive material.

Phosphor screen 30 may be replaced by an electronic scanning device suchas an electron bombardment induced conductivity target and a televisionscan readout, such as used in vidicons, image orthicons, etc. Theconductivity target may have a resistor backing with four electrodespositioned thereon to detect the position of the correlation spot.Phosphor screen 30 may also be optically coupled to a television pick-uptube.

The present invention may be used in a system for automatic tracking ofscenes, such as would be used in an electro-optically guidedair-to-surface missile. Since the image in this case will not onlyexperience translational motion on photocathode 16, but considerableother changes such as magnification, it is necessary to up-date thestored reference image on storage screen 22 periodically. This up-datingcan be done most accurately if the correlation spot is exactly in thecenter of phosphor screen 30 or the other device that may replace it.For low-light level images tube 10 may contain one or more intensifiersections between photocathode 16 and accelerator 20.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

l. The method of electronically correlating two images comprising thesteps of:

a. uniformly illuminating a direct view type storage tube,

b. adjusting the electrode voltages of the tube to remove all chargesfrom the storage screen of said storage tube,

0. adjusting the electrode voltages and focusing means to cause an imageof a scene to be optically focused on the photocathode of the tube andto be electronically focused on the storage screen, d. ad usting t eelectrode voltages and focusing means to focus a subsequent electronimage of the scene that is different in size from that focused on to thestorage screen into a plane which is not common with the storage screen,

e. observing on the phosphor screen the point at which electrons arepermitted by the storage screen to impinge on the phosphor screen.

2. The method of electronically correlating two images comprising thesteps of:

a. uniformly illuminating a direct view type storage tube,

b-. adjusting the electrode voltages of the tube to remove all chargesfrom the storage screen of said storage tube,

c. adjusting the electrode voltages and focusing means to cause an imageof a scene to be optically focused on the photocathode of the tube andto be electronically focused on the storage screen,

d. adjusting the electrode voltages and focusing means to focus asubsequent electron image of the scene in a plane between theaccelerating electrode and the focusing screen so that the virtual imageformed is larger than the image on the storage screen,

e. observing on the phosphor screen the point at which electrons arepermitted by the storage screen to impinge on the phosphor screen.

3. The method of electronically correlating two images in a direct viewtype storage tube comprising the steps of:

a. uniformly illuminating the photocathode of said storage tube forremoving all charges from the storage screen of said storage tube,

removing the illuminating source from said photocathode after the chargehas been removed from the storage screen,

c. adjusting the electrode voltages and focusing means to cause an imageof a scene to be optically focused on the photocathode and to beelectronically focused on the storage screen,

. re-adjusting the electrode voltages and focusing means to focus asubsequent electron image of the scene into a plane intermediate saidstorage screen and said photocathode so that the virtual" image formedis larger than the image on the storage screen,

e. observing on the phosphor screen the point at which electrons strikethe screen indicating the point of best match between the two images.

1. The method of electronically correlating two images comprising thesteps of: a. uniformly illuminating a direct view type storage tube, b.adjusting the electrode voltages of the tube to remove all charges fromthe storage screen of said storage tube, c. adjusting the electrodevoltages and focusing means to cause an image of a scene to be opticallyfocused on the photocathode of the tube and to be electronically focusedon the storage screen, d. adjusting the electrode voltages and focusingmeans to focus a subsequent electron image of the scene that isdifferent in size from that focused on to the storage screen into aplane which is not common with the storage screen, e. observing on thephosphor screen the point at which electrons are permitted by thestorage screen to impinge on the phosphor screen.
 2. The method ofelectronically correlating two images comprising the steps of: a.uniformly illuminating a direct view type storage tube, b. adjusting theelectrode voltages of the tube to remove all charges from the storagescreen of said storage tube, c. adjusting the electrode voltages andfocusing means to cause an image of a scene to be optically focused onthe photocathode of the tube and to be electronically focused on thestorage screen, d. adjusting the electrode voltages and focusing meansto focus a subsequent electron image of the scene in a plane between theaccelerating electrode and the focusing screen so that the''''virtual'''' image formed is larger than the image on the storagescreen, e. observiNg on the phosphor screen the point at which electronsare permitted by the storage screen to impinge on the phosphor screen.3. The method of electronically correlating two images in a direct viewtype storage tube comprising the steps of: a. uniformly illuminating thephotocathode of said storage tube for removing all charges from thestorage screen of said storage tube, b. removing the illuminating sourcefrom said photocathode after the charge has been removed from thestorage screen, c. adjusting the electrode voltages and focusing meansto cause an image of a scene to be optically focused on the photocathodeand to be electronically focused on the storage screen, d. re-adjustingthe electrode voltages and focusing means to focus a subsequent electronimage of the scene into a plane intermediate said storage screen andsaid photocathode so that the ''''virtual'''' image formed is largerthan the image on the storage screen, e. observing on the phosphorscreen the point at which electrons strike the screen indicating thepoint of best match between the two images.